Cameras taking pictures at night are widely used, e.g. in outdoor surveillance and hunting monitoring. According to the different nighttime illumination modes, the cameras taking pictures at night could be categorized in two types:
One type uses Xenon flash, also called HID Intensity discharge lamp, as flash to take color photos. While the Xenon flash is used for illumination, High voltage current of thousands of volts stimulates Xenon to illuminate, generating white arcs similar to fluorescent lamp between the two poles, which has good night illumination for clear color photographs. But because there is a strong visible light flashes when photo is taken, animals may be frightened or the attention may be attracted in monitoring, the use has no concealment.
The other type uses infrared LED as illumination source of photos or videos to take black and white images. The infrared LED emits light not through the electronic transitions within the atom, but through adding voltage on the two ends of PN junction, making the PN junction itself to form energy level on which the electrons transit. Based on the light emitting principle of LED, the instant illumination intensity in photo-taking is generally low, far from the high intensity illumination generated by instant high voltage of gas discharge flash, so the images has more noise and it is easy to cause motion blur. But infrared lights emitted by the infrared LED has good concealment, therefore current outdoor surveillance camera and hunting monitoring camera mainly use infrared LED as illumination source.